Microwave ovens



Oct. l 27, 1959 R. v. SMITH 2,910,566

MICROWAVE OVENS Filed June 25, 1958 l N VEN TOR ROBERT V. SMITH HV1/Mw( United States Patent O 2,910,566 MICROWAVE ovENs Robert V. Smith, Marlboro, Mass., assignor to Raytheon Company, a corporation of Delaware Application June 23, 1958, Serial No. 743,693

8 Claims. (Cl. 219-10.55)

This invention relates generally to microwave ovens and more particularly to means for browning foodstuffs to be cooked in said microwave ovens.

One of the principal difficulties in using highfrequency energy for the cooking of foodstuffs has Vbeen the inability of such microwave energy to brown rfoodstuffs such as meats, cakes and pastry. One method that has been used in the pastto overcome this ditculty has been to .provide an relectrical radiant heating means, such as a conventional calrod unit, that can be mounted in the top of the oven cavity. There are a number of disadvantages to using an electrical radiant heating method. One of the principal disadvantages lies in the fact that such a unit is metallic and covers a large percentage of the area through which the high frequency energy must pass. This fact results in a .considerable disturbance in the high frequency energy pattern within the oven cavity and a possible adverse change in the oven impedance. In addition, some of the high frequency energy is apt to leak out through the power lines which supply the electrical power necessary for the radiant heating energy. Because, in many cases, relatively high power is required, the switches used with the electrical unit have to be very ruggedly constructed, and the expense of the entire unit may be relatively high.

This invention provides a microwave oven structure that utilizes a gas broiler unit mounted within the oven cavity itself. .The gas broiler unit is molded from a ceramic having a high alumina content and a low amount ofV metallic impurities. Because ythe unit is made of ceramic material, `there is substantially no distortion of thehigh frequency energy pattern within the oven cavity and, hence, no undesirable adverse change in oven impedance. The unit may be easily fabricated and fitted into a partition between the oven proper and the high frequency lenergy source. Because gas is' used, the broiler is brought upto operating temperature substantially instantaneously, and broiler heating is removed instantaneously when the gas is turned oif. The controls -of the gas are smaller and more reliable than the electrical counterparts at the power levels required. There is no leakage of the high frequency energy and the quantitiesgof .gas vneeded .forbrowning foods are small enough so that bottled gas could be used. In many areas of the country, gas is a more economical source of heating than electricity.

The invention can best be described with the help of the drawing, in which:

Fig. 1 shows a pictorial, cutaway view of an oven configuration and gas broiler unit that represents an embodiment of the invention; and

Fig. 2 shows an enlarged sectional view of a portion of the gas broiler unit of the oven configuration shown in Fig. 1.

In Fig. 1 there is shown a hollow, rectangular, metallic enclosure or cavity which serves as the oven of the heating device. The dimensions of the enclosure are ice preferably, although not necessarily, large compared with the wave length of the high frequency energy used. In order to allow for the insertion or removal of foodstuffs to be heated, an aperture closed by a hinged metal door 15 having a handle 16 is provided at one side of the oven. A source of high frequency energy, such as a magnetron 20, is mounted at top wall 19 of the oven cavity. The magnetron may, for example, have a dome shaped portion 21 which functions as an electromagnetic radiator of energy conducted thereto from the magnetron cavity resonators. Such magnetrons, as well as other types of magnetrons which are also adaptable for use with oven 10, are well known in the art and, therefore, need not be described in detail. Other means of coupling energy into the oven, such as wave guide means, may also be used. Foodstuif 14 to be heated may -be placed on bottom wall 16 of the oven cavity. A stirring means 18 is shown mounted approximately in the center of the top wall of oven cavity 10. "Ihe stirring means is used to excite a large number of modes of high frequency energy within the oven cavity in order to provide uniform heating of foodstuff 14. Such stirring means are not essential to the operation of the invention, although they are generally used in most conventional microwave ovens. A particular example of such an oven conguration and stirring means is described in my patent, Serial No. 414,656, filed March 8, 1954, and issued as Patent No. 2,813,185 on November 12, 1957.

A partition 11 is mounted between the high frequency energy source and the foodstuff to be heated. The partition is molded from a ceramic material having a high alumina content. The ceramic material should also have a very low content of titanium dioxide, which is a relatively lossy material. Partition 11 is mounted so as to provide gas jets 12vat bottom side 13 of the partition. The gas jets are supplied with gas from a source 17 of bottled gas, such as luminating gas, through a pipe 22. The bottled gas is mounted by suitable clamping means 23 to the outside of the oven cavity and pipe 22 is inserted into ceramic partition 11 through an opening 24 in one wall of the cavity. The construction of partition 11 is shown in more detail in Fig. 2`. The partition may be made of a thickness of approximately one-half a wave length of the operating frequency to minimize the reilection coefficient of the partition and aid in impedance matching. However, its exact thickness is not critical and any-mismatching which may occur may be compensated by moving the' partition up or down until optimum matching conditions are obtained. The partition is held at its four corners by metallic pieces 25. Metallic pieces 25 are small enough so that they do not appreciably aiect theV heating pattern of the high frequency energy.

Fig. 2 shows a more detailed sectional drawing of partion 11. The partition is fabricated so as to provide a plurality of parallel channels 26 parallel to one dimension of the partition. Only one of the parallel channels is shown in Fig. 2. A channelA 27' perpendicularto chan; nels 26 is provided at one end of the partition in order to provide a common means of supplying gas to parallel channels 26. Gas pipe 22 extends from source 17 of bottled gas through opening 24 in the side wall of the oven cavity to channel 27. Opening 24 contains a sealing means 28 to prevent the escape of high frequency energy from the oven. Gas jets 12 are provided on bottom side 13 of partition 11 along each of the parallel channels 26. A valve 30 shown in Fig. 1 is mounted at the source of bottled gas so that the gas may be turned on and off when necessary. A conventional pilot light 31 may be provided to ignite the gas when desired. Pilot light 31 is inserted into the interior of oven 10 through opening 32 having a sealing means 33 similar to that provided for gas mpc 22.

The use of such a partition not only provides a source of gas for broiling lorzbrovvning the foodstuffs but also `acts as .an insulator and protector for .the Vhigh frequency energy source. Becauseithe broiler .unit can befabricated from a ceramic exhibiting :a low dielectric constant and a low dielectric loss, `the kefficiency of the oven is -notfimpaired. Asv long as the ceramic contains substantially small amounts of metallic impurities, any danger of eX- plosion due to sparking in the presence or" gas is minimized. The partition in the oven kconfiguration shown inthe figures, of course, does'not represent the only embodiment of this invention. Other structures utilizing the principles of theinvention will occur to those skilled in the art within the scope of this invention. Hence, the invention is not to beconstrued to be limited to the figures shown and herein described except as defined by the appended claims.

What is claimed is:

1. .A microwave oven comprising an oven cavity, means for supplying high-frequency electromagnetic energy to said cavity,.a heating load contained within saidcavity, said load being thereby heated by said source of electromagnetic energy, a partition mounted within said cavity comprising .a plurality of orifices, a source of fuel, means for feeding said fuel from said source to said orifices, means for igniting said fuel at said orifices whereby radiant heat energy is supplied to said heating load.

2. A microwave oven comprising an oven cavity, means for supplying'high-frequency electromagnetic energy to said cavity, a heating load contained within said cavity, said load being thereby heated by said source of electromagnetic energy, a partition mounted within said cavity comprising a plurality of channels having a plurality of orifices, a source of'fuel, meansfor feeding said fuel'from said source to said channels and to said orifices, means for igniting said fuel at said orifices whereby radiant-heat energy is supplied to said'heating load.

3. A microwave oven comprising .an o'ven cavity,.means for supplying high-frequency electromagnetic energy to said cavity, a heating'load contained within said cavity, said'load being thereby heated by said source of electromagnetic energy, a partition mounted within said cavity between said supply means and said heating load comprising a plurality of .channels having aplurality of orifices, a source of fuel,means for feeding said fuel from said source to said .channels and to said orifices, means for igniting said fuel at said orifices whereby radiant heat energy is supplied to said heating load.

4. A microwave oven comprising `an oven cavity, means lfor supplying high-frequency electromagnetic energy to said cavity, a heating load contained within said cavity, said load being thereby heated by said source of electromagnetic energy, a ceramic partition mounted within said cavity between said supply means and said heating load comprising a plurality of channels having ,a plurality of orifices, a source of'fuel, means for feeding said fuel from said source to said channels and to said orifices, means for igniting'said fuel at said orifices whereby radiant heat energy is supplied to said heating load.

5. A microwave oven comprising an oven cavity, a load contained within said cavity, means 'for 'supplying highfrequency electromagnetic energy to said cavity whereby said load is heated by said"highfreq'uency energy, a ceramic partition having a low dielectric constant and a low dielectric loss mounted within said cavity between said supply means and said heating load comprising a plurality of channels having a plurality of orifices, a source of fuel, means for feeding lsaid fuel from V-said'source to said channels and to said orifices, means for igniting said fuel at said orifices whereby radiant heat energy is supplied to said heating load.

6. A microwave oven -comprising `an oven cavity, a mass of foodstuff contained within said cavity, means for supplying high-frequency electromagnetic energy to said cavity whereby said foodstuff is cooked by said highfrequency energy, a ceramic partition having a high alumina content and a low vmetallic impurity content mounted within Ysaid cavity betweensaid supplyrmeans and said heating loadcomprisinga plurality of channels having a plurality'of oritice,s,.a source of fuel, means for feeding said fuel from Vsaid source to said channels and to said orifices, means for ignitingsaidfuel atsaid orifices whereby radiant heat energy .is `supplied to said heating load.

7. A microwave open comprising van oven cavity, means for supplying high-frequency electromagnetic energy to said cavity, a mass of foodstuff contained within said cavity, said foodstuff being thereby cooked by said high-frequency energy, a ceramicy partition having a `low dielectric constant and Ia low dielectric loss mounted within said cavity between said supply means andsaidheating load comprising a plurality of channels having aplurality Vof orifices, a source of luminating gas, means forfeeding said luminating gas from said source to said channels and to said orifices, means for igniting said luminating gas at said orifices whereby radiant' heat energy is supplied to y' said heating load. t

8. A microwave oven comprising an oven cavity, means for supplying high-frequency electromagnetic energy to said cavity, stirring means for exciting a plurality of modes of said high frequency energy, a mass of foodstuff contained within said cavity, said foodstuff thereby being cooked by :said highffrequency energy, va ceramic partition having alow dielectric constant and a low Adielectric loss mounted within said cavity between said supply means and said mass of foodstuff comprising a plurality of channels having applurality of orifices, a source of luminating gas, means for feeding said luminating gas from said source to said channels and to said orifices, means for igniting said luminating gas at said orifices whereby radiant heat energy is supplied to said mass of foodstuff yand the surface of said 'foodstuff is thereby browned. v

References Cited in the file of this patent UNITED STATES PATENTS 1,358,966 Marquardt Nov. 16,1920 2,463,712 Newell Mar. 8, 1949 2,597,825 Schroeder May 20; 1952 2,831,952 Warner ;Apr.f22, 1958 

